The NATO mission in the country issued a statement saying the soldier died during the military operation on Saturday, without providing further details.
President Donald Trump in August approved a Pentagon plan to deploy as many as 3,800 additional US forces to Afghanistan, where there are already more than 11,000 serving.
The US and allied forces are battling a resurgent Taliban as well as an Islamic State affiliate in Afghanistan, which is still gripped by unrest 16 years after the US-led invasion.
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